The present invention relates generally to probes used in collecting and sensing the gas content of liquid, molten metal, and more particularly to a hollow probe providing efficient collection of gas contained in a liquid metal.
It is known that hydrogen dissolved in molten metal, such as aluminum and aluminum alloys, causes voids or pores to develop within an ingot cast from such molten metal, the voids forming during the process of solidification. The voids give rise to various problems in products produced from the solidified metal. There has, therefore, been increasing requirements that a so-called dehydrogenation process be performed, i.e., that hydrogen dissolved in molten metal be removed as an important step in metal casting processes.
Before any removal of hydrogen gas takes place, of course, it is necessary to determine whether or not a body or supply of molten metal contains sufficient amounts of hydrogen for the removal process. This determination can be made by hydrogen sensing apparatus, such as those disclosed in the following U.S. Pat. Nos.:
2,861,450--Ransley PA1 4,454,748--Warchol et al PA1 4,731,732--Terai et al PA1 4,829,810--Anderson et al PA1 4,907,440--Martin et al
The disclosures of these patents are incorporated herein by reference.
In the above references, the content of hydrogen dissolved in a body of molten metal is determined by directing an inert carrier gas into the molten metal, and circulating the carrier gas a substantial number of times in the metal. In the process, the carrier gas acquires hydrogen gas from the molten metal when it is first brought in contact with such metal, and the acquired hydrogen content in the carrier gas increases in each period of contact until the hydrogen partial pressure in the carrier gas equilibrates with the hydrogen partial pressure in the metal.
Generally, the number of contacts required between the carrier gas and the liquid metal is relatively large before equilibrium is reached. A pump is used for this process to circulate the mixture of carrier gas and hydrogen content to and through a hydrogen sensing device and to and from the liquid metal.
Carrier gases are conducted into liquid metals and removed therefrom by hollow probe devices, such as shown in the above-incorporated patent references using pumps, tubing and check valves that control the direction of carrier gas to and from the liquid metal.